This invention relates to the growth of cubic boron nitride (CBN) crystals as clusters of crystals.
The use of seeds to control crystallisation by controlling the number of nucleation sites is well known in the art of crystal growing. In the case of cubic boron nitride synthesis, small cubic boron nitride particles may be used as seeds to promote the preference of crystal growth on the seeds rather than crystal growth by spontaneous nucleation. For such applications, it is desirable to ensure that the seeds have a known size distribution, so that numbers of seeds can be controlled, and that the seeds are distributed evenly and discretely.
Generally, in the art of growing cubic boron nitride crystals by high pressure, high temperature (HPHT) synthesis, the seeds may be cubic boron nitride particles which are single crystals selected on the basis of size alone. Such seeds are usually made by crushing larger cubic boron nitride crystals or may be as-grown cubic boron nitride crystals, and the cubic boron nitride crystals grown using these seeds are dominated overwhelmingly by single crystals. A method of growing cubic boron nitride crystals uses the difference in solubility between hexagonal boron nitride and cubic boron nitride under the same conditions of pressure and temperature as the driving force for crystallisation.
This method is otherwise known as the allotropic change method. Other methods of generating supersaturation are known in the art. Generally, the objective of such cubic boron nitride growth is to maximise the proportion of individual and discrete crystals, and to minimise the proportion of clusters containing a plurality of crystals. Such clusters, when they occur, may be due to secondary nucleation on the surface of growing crystals, or may be due to the accidental proximity of two or more seeds and/or growing crystals.